We will continue to study the biochemical basis of spontaneous mutation. Our work will continue in 3 specific directions. 1) Using amber mutants of gene 43 in T4 phage, we will compare the genetics and enzymology of specific amino acid substitutions resulting from the growth of these mutants on 3 different suppressors. 2) We will continue to investigate the biochemical basis of the known mutator genes in E. coli. Specifically, we will investigate Mut U, Mut S and Mut T. 3) We will try to develop an in vitro test for mutators and antimutators based on the amount of incorporation of the analogue 2-aminopurine deoxynucleoside triphosphate into DNA.